CH. V] ISOTONIC COEFFICIENT. 115 



dandelion is split longitudinally into four strips which, on 

 being dipped for a moment into water, curl up into 

 spirals and can then be cut up into some 7 or 8 rings, 

 b, fig. 21 : these are delicate tests of changes in turgescence 

 since a small increase or decrease in the curvature of the 

 turgescent tissue is at once perceptible. Thus s is in too 



to h 



FiQ. 21, Exp. 148. 



strong a solution, w is in too weak a solution, while h is 

 in one that almost exactly balances the osmotic power of 

 the cell sap. 



The ^dcess with Rieinus is a little more troublesome ; 

 the hypocotyl is split in 4 or more longitudinal portions, 

 and the form of each is traced with a paint-brush (which 

 answers better than a pencil) on paper. We now have a 

 number of curved bits of tissue (whose form is known) 

 each one of which must be placed in a solution of a 

 different strength. These solutions are made according 

 to equivalents, and in the case of KNO3 (which forms the 

 standard) may contain 005, OlO, Oil, 0-12, 013, 014 

 gram-molecules per liter ; stronger solutions may however 

 be needed. After a quarter of an hour the result may 

 be noted : if the material consist of dandelion rings the 

 result is obvious on inspection ; with Rieinus the seg- 

 ments must be compared with the sketches. 



8—2 



